This invention relates to a numerical control device for controlling numerical control machine tools adapted to perform three-dimensional machining operations, and more particularly to a numerical control device for controlling the tool feeding speeds of such numerical control machine tools.
Interactive numerical control devices have been disclosed in Japanese patent application publication (OPI) No. 6784/1978 (corresponding to U.S. Pat. No. 4,477,754) (the term "OPI" as used herein means "an unexamined published application"), and U.S. Pat. No. 4,490,781. In the conventional interactive numerical control devices, as shown in FIG. 1, the operator 1 inputs a command for a tool feeding speed in an interactive mode, using a key board 3 and a display screen 4 on the front panel of the numerical control device 1, or the operator inputs such a command using a paper tape according to an expression method using word addresses (F codes). In this operation, the tool feeding speed is determined according to the operator's experience. When the tool feeding speed becomes unsuitable during machining, the operator 1 adjusts the speed manually with an override dial 5.
The above-described conventional numberical control devices are disadvantageous in the following respects: In the devices, even whenthe amount of machining per unitary length of a tool path is changed during machining, the tool feeding speed is maintained unchanged, and therefore the operator 1 must adjust the tool feeding speed using the override dial 5 during machining. If the amount of machining is very small, then it is difficult for the operator to adjust the tool feeding speed. For instance, in the case where the tool path, as shown in FIG. 4A, is of a pattern of "go" and "return" cutting, although the amount of machining 7 of the first machining unit 6a shown in FIGS. 5A and 6A is different from that of the second machining unit 6b shown in FIGS. 5B and 6B, the tool feeding speed is maintained unchanged. Therefore, the load applied to the tool in the former case is different from that applied to the tool in the latter case, with a result that the surface of the workpiece shows nonuniform finish. This will adversely affect the service life of the tool.